I am an economist so I know some maths but a lot of it is way beyond me. I joined because I trying to find an answer to a simple question in calculus, which I can't seem to find anywhere.

The question is: how do you differentiate the integral of a composite function? Specifically, if what is ?

The closest thing to an answer I could find was Leinbniz's rule, which suggested the answer should be , but the answer I should get (according to someone else's notes) is just , as if the integral isn't there.